Broadband flow-induced sound control using plasma actuators

Plasma actuators were used in this work to control flow-induced broadband noise radiated from a bluff body. The model consists of a cylinder and a component (torque link) that is installed on the lee side of the cylinder. The objective is to reduce the broadband noise mainly generated through the impingement of the cylinder wake on the torque link. The flow-structure interactions between the cylinder wake and the torque link are reduced by manipulating the cylinder wake with the externally imposed body force from the plasma actuators, which lead to the attenuation of the broadband noise. The control performance with the plasma actuators is studied in an anechoic chamber facility by examining far-field sound level and near-field acoustic source changes. At a free stream speed of 30 m/s, corresponding to the Reynolds number of 2.1×10⁵, far-field measurements suggested that a reduction of up to 3.2 dB in overall sound pressure level. The near-field beamforming results also show approximately 3 dB reduction in the interested frequency ranges. The physical mechanisms related to broadband noise control were also discussed. This work suggests that plasma actuators offer the potential for solving flow-induced noise control problem at broadband frequencies.     

Measuring,modelling and optimising an embedded rail track

A finite element (FE) model and a boundary element (BE) model have been developed to predict the decay rate, vibration and noise responses of an embedded rail track. These models are validated using measured results. The optimisation of the embedded rail track is conducted using these calculated models. The results indicate that the optimised cross-section of the gutter for the embedding rail can significantly reduce the radiated noise of the embedded rail track. The embedded rail track using the I-shaped cross-section gutter reduces the radiated noise of the track by at least by 3 dB(A). Furthermore, combining the material parameter optimisation with the gutter cross-section optimisation can further reduce the radiated noise of the embedded rail track. Increasing the Young’s modulus of the rail pad in the embedded rail track with the I-shaped cross-section gutter can result in a radiated noise reduction of 4 dB(A).     

A tuned damping device for reducing noise from railway track

A promising means to reduce the component of railway rolling noise radiated by the track is to increase the damping of the rail. This increases the attenuation with distance of vibrations transmitted along the rail and thereby reduces the noise radiated. To achieve this, a tuned, damped mass-spring absorber system has been designed. To cover a wide range of frequencies, multiple tuning frequencies are used along with a material with a high damping loss factor. Suitable materials have been found from extensive tests on samples and prototypes of the damper have been built and tested, both in the laboratory and in the field. Results are very promising with reductions of the track component of noise of around 6 dB being measured.     

Active absorption to reduce the noise transmitted out of an enclosure

This paper investigates the potential of active absorbers for reducing low-frequency noise transmission through an enclosure. Active absorbers are intended to obtain a purely real prescribed impedance at the front face of a porous layer. This is achieved by an active control system which cancels the acoustic pressure at the rear face. The test bench was a simplified enclosure: a rigid-wall cavity coupled to a baffled elastic plate. The modeling of the system was based on an analytical modal approach. The purpose of this simulation was first to calculate the optimal impedance, providing maximal reduction in radiated power, and then to define a sub-optimal strategy for actual absorber production. Two 3-cell configurations were implemented on the test bench. Active control used a multichannel feedforward algorithm. In line with prediction, the absorbers provided a 5.5 dB overall reduction while covering only 2% of the cavity surface.     

Investigation of rail noise and bridge noise using a combined 3D dynamic model and 2.5D acoustic model

Bridge noise and rail noise are two major sources of an elevated rail transit bridge in the low and medium frequency range (20–1000 Hz). However, in most of the existing literature, the noise radiated from the bridge and rail was investigated separately or using a simplified source model. In this study, an accurate method is proposed to simulate both the rail noise and bridge noise simultaneously. First, the dynamic responses of the rail and multi-span bridge are obtained using a three-dimensional (3D) vehicle-track-bridge interaction analysis model. Then, the two-dimensional (2D) infinite element model is used to calculate 3D modal acoustic transfer vectors of the rail and bridge based on the wavenumber transformation, in order to overcome the singularity and non-uniqueness of the conventional boundary element method and reduce the computation cost. Third, a field test is conducted, and the accuracy of the proposed simulation procedure is verified. Finally, the contribution of the rail and bridge noise to the total noise level is investigated in the whole space near the bridge. Generally the bridge noise occupies a higher contribution in the space beneath the girder due to the shielding effect of the bridge shape on the rail noise, while the rail noise is dominant in the upper space above the bridge. It is found the presence of the vehicle bodies has considerable effect on the rail noise but little influence on the bridge noise. The slope of the roughness level spectrum has significant influence on the dominant field of bridge noise and rail noise. For the excitation of the assumed ISO roughness level used in this study, the difference between the rail noise and bridge noise is only about 3 dB at field points 15–30 m away from the track center, which indicates both the bridge and rail noise should be included in the noise prediction for an elevated rail transit bridge.     

Rotating magnetic macrospheres as heating mechanism for remote controlled drug release

A permanent magnetic macrosphere (diameter: 5 mm) spherically seated in an oil bearing inside an experimental capsule (comparable to a hard gelatine capsule size 2) is turned by a rotating magnetic field (H ? 5 kA/m; frequency ν?500 Hz) and causes a temperature rise up to about 60 °C. In order to find further possible improvements, the experimental results were compared to theoretical expectations. First experiments using improved thermal isolation yielded temperatures of about 100 °C. The heating can be used as a mechanism to remotely release drugs in the gastrointestinal tract.     

Design and performance of a small-scale aeroacoustic wind tunnel

The D5 aeroacoustic wind tunnel at Beihang University is a newly commissioned small-scale closed-circuit wind tunnel with low turbulence intensity and low background noise. The wind tunnel is built to study both aerodynamic and aeroacoustic performance of aircraft components or scaled models. The wind tunnel has two types of test sections, the closed type test section is used for aerodynamic tests while the open type test section is mainly used for aeroacoustic experiments. Both types of test section are 1 m in height and 1 m in width, and the maximum wind velocity in the test section can be up to 80 m/s. An anechoic chamber is built surrounding the test section to provide the non-reflecting condition. This paper provides an overview of design criteria and performance of the small-scale wind tunnel. The layout of the wind tunnel and some critical design treatments to improve aerodynamic and acoustic performance are discussed in detail. Some experiments are conducted to verify the performance of D5 wind tunnel, results confirm that the turbulence intensity is less than 0.08% in the core of test section and the background noise is comparable with other aeroacoustic wind tunnels. A scaled simplified nose landing gear model is also measured as a benchmark test, results reveal that noise radiated from the model is adequately higher than the background noise for a wide frequency range and remarkably consistent with other results from literatures.     

Active noise control of a diesel generator in a luxury yacht

Active noise control has been applied to a variety of systems in order to improve performance without the increases in size and weight that would otherwise be required by traditional passive noise control treatments. This paper investigates the application of an active noise control system to the control of generator noise in the master cabin of a luxury yacht. A multichannel, multi-tonal active noise control system employing loudspeakers and microphones in the master cabin of the yacht is investigated. It is shown that, due to the high number of engine orders produced by the generator, in order to achieve significantly perceptible levels of noise attenuation it is necessary to control at least 7 individual orders. A controller is investigated which targets 19 engine orders and it is shown to achieve in excess of 5 dB broadband attenuation, whilst achieving up to 23 dB attenuation in individual orders. This corresponds to a 23% reduction in the Zwicker loudness.     

Noise source identification for mechanical systems generating periodic impacts

For mechanical systems generating periodic impacts, classical noise source identification approaches are faced with several difficulties. An alternative approach has been developed. First, the radiated sounds under impact excitation of the various system elements are measured. Second, their contribution to the overall system noise is obtained using a signal processing method to extract the various impact source signatures from the overall signal. The approach has been validated progressively in three steps: first, with a numerical simulation, second, with a first experimental set-up where impact sources can be easily added or removed, and, third, with a second experimental set-up closer to industrial reality. The prediction error was found to increase between the simulation and the experimental validations, from <1 dB to values between 1 and 3 dB, which are still acceptable for noise source identification in practice.     

An approach to enhance the receiver sensitivity with SOA for optical communication systems

In this paper, we investigate an SOA (semiconductor optical amplifier) preamplifier structure by optimizing the carrier lifetime in order to reduce the amplified spontaneous emission (ASE) noise and crosstalk, with adequate gain increase. This proposed SOA optical preamplifier has no need of optical alignment and antireflection coating. This structure of SOA eliminates the need of optical filter, and exhibits large tolerance to the input light wavelength. The receiver sensitivity is investigated for single and multi channel transmission links. The received power of − 50.34 dBm is observed at bit error rate (BER) 10^− 12 for 10 Gb/s with PIN receiver. Further, the impact of gain, amplified spontaneous emission power and gain variation for different carrier lifetime with input power for OOK system is illustrated. The proposed SOA has constant gain of 30.06 dB up to gain saturation for carrier lifetime 0.18 ns. It is predicted that low value of carrier lifetime suffers less from ASE noise.     

Performance of a snoring noise control system based on an active partition

This paper proposes an active partition that can be placed between a snorer and a non-snorer on a bed to reduce the snoring noise around the non-snorer ears by integrating a rigid finite size passive partition with a two channel active noise control system. The noise reduction performance of the passive partition on a bed with a headboard is studied first, where the effects of the height and the width of the partition are discussed. Due to the limited partition size, the attenuation for the low-frequency diffracted noise is not sufficient, so two loudspeakers are proposed to be installed on the partition as the secondary sources to increase the overall noise attenuation. Both numerical simulations and experiments are carried out to demonstrate the feasibility of the proposed integrated snoring noise control system, and the results show that the proposed active partition can achieve over 10 dB noise attenuation at non-snorer ears in the 1/3 octave bands from 80 to 1000 Hz.     

Analysis and minimization of cross phase modulation in semiconductor optical amplifiers for multichannel WDM optical communication systems

A theoretical model for crosstalk in multichannel wavelength division multiplexing communication systems due to cross phase saturation in semiconductor optical amplifier structure is developed. This theoretical model is used to analyze the impact of the cross phase noise on the performance of semiconductor optical amplifiers in saturation region for WDM communication system by using differential phase shift modulation format. It is shown that by increasing the carrier life time, width and thickness while reducing the confinement factor, differential gain and bias current in the SOA structure mitigates the cross talk due to cross phase saturation. The impact of penalty and cross phase noise imposed on multichannel WDM links have been investigated for different parameters of the SOA with the variation in transmission distance. With the slight increase in differential gain of 200.2 × 10⁻¹⁸ cm² and confinement factor 0.41, the maximum transmission distance observed is 5220 km with good quality and nil power penalty for 10 × 40 Gb/s soliton RZ-DPSK WDM signals for the first time.     

Reduction of radiated exterior noise from the flexible vibrating plate of a rectangular enclosure using multi-channel active control

This study attempted to control the radiated exterior noise from a rectangular enclosure in which an internal plate vibrates by acoustic excitation and noise is thus radiated from that plate. Multi-channel active control was applied to reduce the vibration and external radiation of this enclosed plate. A piezoelectric ceramic was used as a distributed actuator for multiple mode control of the vibration and radiated noise in the acoustically excited plate. To maximize the effective control, an approach was proposed for attachment the piezoelectric actuator in the optimal location. The plate and internal acoustic space in the enclosure are coupled with each other. This will change dominant frequency characteristics of the plate and, thus, those of the externally radiated noise. Active noise control was accomplished using an accelerometer attached to the plate and a microphone placed adjacent to that plate as an error sensor under acoustic excitation of sine wave and white noise. It was found that the control of radiated external radiation noise requires a microphone as an error sensor, a sound pressure sensor due to vibration of the plate, differences in the dominant frequency of externally radiated noise, and complex vibration modes of the plate.     

Performance evaluation of IDW,Kriging and multiquadric interpolation methods in producing noise mapping: A case study at the city of Isparta,Turkey

In order to produce an accurate noise map of a city or a region, it is necessary to make noise measurements at certain locations and these measurements must be modeled with the most suitable mathematical algorithm. A homogeneous and representative distribution of the noise measurement points is the first key factor in the production of sound noise maps. The second key element is the calculation of the noise values of gridding points based on noise measurement points according to the selected mathematical calculation method and the generation of maps according to these gridding points. In this study, a noise map of the Isparta city center and its periphery was produced using inverse distance weighted (IDW), Kriging and multiquadric interpolation methods with different parameters and four grid resolution. Then, the influence of parameter selection for each method was investigated in themself by taking into account grid resolution, namely 10 ∗ 10 m, 50 ∗ 50 m, 100 ∗ 100 m and 200 ∗ 200 m, and the performance of three method with 50 ∗ 50 m grid resolution were compared with each other. In addition, the noise mapping of the city of Isparta were produced by Kriging method with respect to maximum, average and minimum noise data and they were evaluated by considering the national environmental noise thresholds.     

Thermally tunable microfiber knot resonator based erbium-doped fiber laser

A compact and tunable erbium-doped fiber laser is demonstrated using a highly doped fiber and a microfiber knot resonator (MKR) structure which is laid on the surface of a small peltier. The MKR functions as both a reflector and a tunable filter where tunability is achieved by varying the temperature of the resonator by heating the peltier. A stable laser output is achieved at the 1533 nm region with an optical signal to noise ratio (OSNR) of 27 dB using a 65 mW of 980 nm pump power. The operating wavelength of the laser can be tuned from 1532.60 nm to 1533.49 nm as the temperature is increased from the room temperature of 24 to 90 °C. It is observed that the operating wavelength shifts to a longer wavelength as the temperature increases with an efficiency of 12.4 pm/°C. This is due to the thermally induced optical phase shift attributable to the changes in effective refractive index and optical path length of the MKR loop.     

A full-scale test rig for railway rolling noise: simulation and measurement of dynamic wheelset-track interaction

A new outdoor rolling-noise test rig on a 25 m stretch of full-scale track will enable the study of vibrations of wheel and rail and of the pertinent noise emission under controlled conditions. The arrangement can be seen as a physical realization of the Track-Wheel Interaction Noise Software (TWINS) computer software. The track and wheel, which are not in mechanical contact, are excited in vertical and lateral directions using electrodynamic actuators. The track can be statically pre-loaded by up to 30 tonnes. The use of the rig is presently under development. The aim is that the radiated noise from separate railway components could be found as the wheel and the track can be excited both together and separately. Amplitude and phase of the applied forces are predetermined by use of an algorithm taking into account the real wheel-rail interaction properties. In that way different wheel-rail contact conditions can be simulated. Eight partners have co-operated in the development and operation of the CHARMEC/Lucchini Railway Noise Test Rig in Surahammar, Sweden.In ongoing experiments, the dynamics of both the wheel and rail have been examined in the frequency domain. For the track, comparisons have been made between data obtained from the rig and those from field measurements on a standard Swedish line. Both dynamic response and spatial decay rates have been studied. The performance of the rig has also been compared to results from TWINS and to results from the literature. Good agreement was obtained in the frequency range from 100 to 5000 Hz. Some results from preliminary measurements of noise emission will be given.     

Reduction of vibration and noise radiation of an underwater vehicle due to propeller forces using periodically layered isolators

Using periodic structure theory, the suppression of vibration and noise radiation from an underwater vehicle due to excitation from propeller forces is investigated. The underwater vehicle is modelled in two parts (the hull and the propeller/shafting system). A model of the propeller/shafting system is constructed using a modular approach and considers the propeller, shaft, thrust bearing, isolation structure and foundation. Different forms of isolator are considered – a simple spring-damper system, a continuous rod and a periodically layered structure. The dynamic properties of the underwater vehicle and the isolation performances of various isolators are compared and analysed. The stop band properties of the periodic isolator are used to enhance the passive control performance. Furthermore, an integrated isolation device is proposed that consists of the periodic isolator and a dynamic absorber, and its isolation performance is investigated. The effects of the absorber parameters on the performance of the integrated device are also analysed. Finally, the radiated sound pressure is calculated to verify the attenuation. The numerical results show that the vibration and noise radiation are greatly attenuated in the stop bands. By optimising the design of the periodic isolators and its integrated structures, the suppression of the vibration and noise radiation can be improved effectively.     

On vortex–airfoil interaction noise including span-end effects,with application to open-rotor aeroacoustics

A linear analytical model is developed for the chopping of a cylindrical vortex by a flat-plate airfoil, with or without a span-end effect. The major interest is the contribution of the tip–vortex produced by an upstream rotating blade in the rotor–rotor interaction noise mechanism of counter-rotating open rotors. Therefore the interaction is primarily addressed in an annular strip of limited spanwise extent bounding the impinged blade segment, and the unwrapped strip is described in Cartesian coordinates. The study also addresses the interaction of a propeller wake with a downstream wing or empennage. Cylindrical vortices are considered, for which the velocity field is expanded in two-dimensional gusts in the reference frame of the airfoil. For each gust the response of the airfoil is derived, first ignoring the effect of the span end, assimilating the airfoil to a rigid flat plate, with or without sweep. The corresponding unsteady lift acts as a distribution of acoustic dipoles, and the radiated sound is obtained from a radiation integral over the actual extent of the airfoil. In the case of tip–vortex interaction noise in CRORs the acoustic signature is determined for vortex trajectories passing beyond, exactly at and below the tip radius of the impinged blade segment, in a reference frame attached to the segment. In a second step the same problem is readdressed accounting for the effect of span end on the aerodynamic response of a blade tip. This is achieved through a composite two-directional Schwarzschild's technique. The modifications of the distributed unsteady lift and of the radiated sound are discussed. The chained source and radiation models provide physical insight into the mechanism of vortex chopping by a blade tip in free field. They allow assessing the acoustic benefit of clipping the rear rotor in a counter-rotating open-rotor architecture.     

Space-time and hybrid algorithms for the passive acoustic localisation of sperm whales and vessels

In the frame of the European Sea-floor Observatory Network (ESONET) and in preparation of the Demonstration Mission Listening to the Deep-Ocean Environment (LIDO) algorithms for the automated real-time detection, classification and localisation of cetaceans have been developed.Such Passive Acoustic Monitoring techniques have the potential to play a key role in cetaceans’ conservation for they allow a non-invasive study of their behaviour, a better knowledge of their population dynamics, and a better understanding of their dynamic relationship with their environment. This paper investigates the development of efficient and accurate techniques to be used as the basis of a localisation module for an automated real-time Passive Acoustic Monitoring system.An opportunity to assess the capabilities of the developed localisation modules was given by recordings collected with a bottom-mounted (around 2080 m depth) tetrahedral compact hydrophone array located offshore the port of Catania (Sicily) during the NEMO-ONDE campaign in the years 2005-2006 by INFN and CIBRA [2]. A well-known class of methods for acoustic source localisation is based on time differences of arrival (TDOA). Its capabilities have shown to be useful even in adverse situations (i.e., few sensors, high noise levels and/or poor calibration). A second class of methods, the space-time methods, originated in underwater applications such as sonar but reached its most significant achievements over the last 20 years in digital communications with recent progress in the treatment of broadband signals. These developments are here revisited under the scope of the localisation and tracking of cetacean vocalisations.Various broadband space-time methods were implemented and allowed to map the sound radiated during the detected clicks and to consequently localise both sperm whales and vessels. Hybrid methods were also developed which improved the robustness of space-time methods to noise and reverberation and reduced processing time. In most cases, the small variance obtained for these estimates lessened the necessity of additional statistical clustering. Even though not independently confirmed by sightings, the tracks derived in the proposed frame can be considered to be consistent with the known movements of sperm whales and vessels.     

Design and performance of an open jet wind tunnel for aero-acoustic measurement

This paper presents the design and performance of an open jet, blow down wind tunnel that was newly commissioned in the anechoic chamber at the ISVR, University of Southampton, UK. This wind tunnel is intended for the measurement of airfoil trailing edge self-noise but can be extended to other aeroacoustic applications. With the primary objectives of achieving acoustically quiet and low turbulence air jet up to 120 m/s through a 0.15 m × 0.45 m nozzle, several novel noise and flow control techniques were implemented in the design. Both the acoustical and aerodynamic performances of the open jet wind tunnel were examined in detail after its fabrication. It is found that the background noise of the facility is adequately low for a wide range of exit jet velocity. The potential core of the free jet is characterized by a low turbulence level of about 0.1%. Benchmark tests by submerging a NACA0012 airfoil with tripped and untripped boundary layers at 0° and 10° angles of attack respectively into the potential core of the free jet were carried out. It was confirmed that the radiating airfoil trailing edge self-noise has levels significantly above the rig noise over a wide range of frequencies. The low noise and low turbulence characteristics of this open jet wind tunnel are comparable to the best facilities in the world, and for its size it is believed to be the first of its kind in the UK.